Do I break it to my son or just let him figure things out for himself..

My son is 9yo. Got his 1st lil “girlfriend” last school year. They were really close. Her mom & I ended up homeschooling together this year & I thought we were closer than we were apparently. Recently the mom straight up ghosted everyone. I know they planned on moving at some point, but they were nowhere near ready. It’s been a month. She isn’t returning calls or texts. Just completely ghosted everyone. Not only am I worried, but I’m upset is for the kids. Not to mention, now she’s put us in a hard situation because our son needs closure. That girl & her brother were his best friends. He’s an only child. So when I overheard my son talking to his friends about his GF today, it broke my heart. He doesn’t understand that he will never see or hear from her or her brother ever again. That the last time he saw her was the last memory he will ever have with them. I feel guilty too because when the kids were having a hard time accepting that they weren’t going to live near us anymore, I promised that we were going to visit since they won’t be far. I know it doesn’t seem that deep, they’re 7-9yo. But my child has BIG feelings & these kids meant ALOT to him. Idk how to approach this situation with him.